The present invention relates to an improved copper chromite catalyst which shows much greater activity in reducing an aldehyde to an alcohol than copper chromite catalysts known in the prior art. Specifically, the copper chromite catalyst of this invention allows the production of furfuryl alcohol at pressures which are much below those pressures for batch preparation of furfuryl of the prior art. The sintering temperature at which the copper chromite catalyst is formed, by decomposition of a copper ammonium chromite complex, is believed to be responsible for the increased activity of the catalyst.
It is known that a copper chromite catalyst may be prepared in the following manner. Copper sulfate, CuSO.sub.4.5H.sub.2 O, and sodium dichromate, Na.sub.2 Cr.sub.2 O.sub.7.2H.sub.2 O, can be combined with ammonium hydroxide to form a complex from which copper chromite may be prepared. The copper sulfate and sodium dichromate are dissolved in water to form a solution. To this solution ammonium hydroxide is added until the pH reaches 7.0 to 7.5 A precipitate is formed which is a complex and according to the literature has the formula Cu(OH) NH.sub.4 CrO.sub.4. This complex is purified and used to prepare copper chromite. It is believed that the following equation represents the formation of the complex: EQU 2 CuSO.sub.4.5H.sub.2 O+Na.sub.2 Cr.sub.2 O7.2H.sub.2 O+4NH.sub.4 OH.fwdarw.2 Cu(OH)(NH.sub.4)CrO.sub.4 +Na.sub.2 SO.sub.4 +(NH.sub.4).sub.2 SO.sub.4 +13H.sub.2 O (1)
The production of copper chromite is carried out by decomposing the complex by heat. The formula for the decomposition reaction described by the prior art is as follows: EQU 2Cu(OH)NH.sub.4 CrO.sub.4 .fwdarw.Cr.sub.2 O.sub.3.2CuO+N.sub.2 +5H.sub.2 O(2)
The above reaction (1) is known to be highly exothermic. The decomposition reaction begins when the temperature of the complex reaches approximately 230.degree. C. Because of the exothermic nature of the reaction it is also self sustaining. It is known that if the temperature at which the decomposition reaction (2) occurs is allowed to reach a temperature of 400.degree. or above that the copper chromite catalyst produced will have diminished activity and accordingly the decomposition reaction temperature was controlled so that the temperature at which the reaction (2) takes place is below 400.degree. C. The prior art copper chromite catalysts formed as described typically have a low loss on ignition and a highly crystalline structure.
Copper chromite catalysts prepared as described above are known to be useful as catalysts for reducing aldehydes to alcohols in the presence of unsaturation. This knowledge has direct application to the production of furfuryl alcohol from furfural. The prior art teaches that the reduction of furfural to furfuryl by hydrogenation using a liquid phase process and using copper chromite as a catalyst will occur at 100 atmospheres and at temperatures of 200.degree. C. or less. This process is said to give almost quantitative yields of furfuryl alcohol.
It is further known that calcium oxide, CaO, is useful in this reaction to improve the selectivity of the reaction. The use of calcium oxide is desirous since this compound prevents the formation of ethers. Ethers may be formed in this reaction after furfuryl alcohol is formed. Apparently calcium oxide is able to prevent the conversion of alcohol into ether and thus improves the selectivity of the preparation of furfuryl alcohol. It appears that other metal oxides may also accomplish this function. It is not believed that the metallic oxides have any effect upon the reaction (3), catalytic or otherwise, other than the improvement of selectivity, but the mechanism is unknown.
It is desirable to improve the prior art liquid phase methods of preparing furfuryl alcohol from furfural. One disadvantage of the prior art is that high pressure, 100 atmospheres or more, is required.
Accordingly, it is an object of this invention to provide a catalyst which allows the liquid phase preparation of furfuryl alcohol from furfural at pressures lower than those of the prior art. The object described above is ideally reached without sacrificing the quantitative yield of furfuryl alcohol and without decreasing the rate of conversion at the catalyst levels of the prior art.